An electrophotographic image forming apparatus is known in which a photosensitive member is charged with a corona charger. In particular, a product using a corona charger called a scorotron which is provided with a grid so as to stabilize a charged potential of the photosensitive member is known. In such a structure, in order to efficiently and uniformly charge the photosensitive member, arrangement of the grid of the corona charger in close proximity to the photosensitive member is known.
The fact that the corona charger charges the photosensitive member along with corona discharge is known. When corona discharge occurs in air, discharge products (ozone, nitrogen oxide, etc.) are generated. When the discharge products are deposited on the photosensitive member, the discharge products absorb moisture in a high humidity environment, thereby causing an image defect called image deletion.
On the other hand, heating the photosensitive member with a heater to suppress moisture absorption of the discharge products and suppress occurrence of image deletion has been considered. However, in terms of energy saving, it is not desirable to continuously to heat the photosensitive member with the heater so as to suppress occurrence of image deletion.
PTL 1 as identified below discloses a structure in which an opening of a corona charger that faces a photosensitive member is shielded with a shutter. Specifically, a carriage that supports an end portion of the sheet-shaped shutter is moved in the longitudinal direction of the opening and, while an image is not being formed, the opening is shielded so as to suppress deposition of discharge products onto the photosensitive member.